FUNZIONE DEL BOSCO NELLA FASE DI ARRESTO DEI DEBRIS FLOW

Debris flows, a flowing mixture of sediments, water, air and other materials, are one of the most destructive events in mountain areas: damaged buildings, interrupted infrastructures, fatalities are only some examples of their effects . In Northern Italy, for example, 36% of fatality events in the field of hydro-geo-morphological hazards is represented by debris flows. Alluvial fans, which have been just built by debris flow events occurred in the past, in fact, are areas where human activities (homes, factories, etc.) have always been developed. People living in mountain areas, in this way, must adopt expensive and impacting technical devices to prevent or to mitigate this phenomena. When the magnitude of debris flow is quite small, the protective capability of forests can be used to mitigate their destructive power. Due to the cost and to the environmental impact associated to the technical works, public administration in some areas of the Alps developed knowledge and guidelines to manage forests in a protection perspective. Few studies concerning the quantification of the protection effect, however, have been carried out especially for debris flow phenomena. In the present work small scale tests have been carried out in order to quantify the wood\u2019s effect in the process of debris flows deposition. Results, in particular, show that trees can significantly influence deposit\u2019s run out and area (two of the main debris flow\u2019s deposition parameters), if their density is appropriate with respect to debris flow characteristics. Such evidence should represent the starting point for future researches which aspire to develop guidelines for protection forest\u2019s maintenance in mountain areas

Root cohesion of forest species in the Italian Alps

Forests can prevent and/or mitigate hydrogeomorphic hazards in mountainous landscapes. Their effect is particularly relevant in the case of shallow landslides phenomena, where plants decrease the water content of the soil and increase its mechanical strength. Although such an effect is well known, its quantification is a relatively new challenge. The present work estimates the effect of some forest species on hillslope stability in terms of additional root cohesion by means of a model based on the classical Wu and Waldron approach (Wu in Alaska Geotech Rpt No 5 Dpt Civ Eng Ohio State Univ Columbus, USA, 1976; Waldron in Soil Sci Soc Am J 41:843-849, 1977). The model is able to account for root distribution with depth and non-simultaneous root breaking. Samples of European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst.), European larch (Larix decidua Mill.), sweet chestnut (Castanea sativa Mill.) and European hop-hornbeam (Ostrya carpinifolia Scop.), were taken from different locations of Lombardy (Northern Italy) to estimate root tensile strength, the Root Area Ratio and the root cohesion distribution in the soil. The results show that, in spite of its dramatic variability within the same species at the same location and among different locations, root cohesion can be coherently interpreted using the proposed method. The values herein obtained are significant for slope stabilisation, are consistent with the results of direct shear tests and back-analysis data, and can be used for the estimation of the stability of forested hillslopes in the Alps